1849, from development + -al (1). Developmentalist (1862) was a word for "follower of the theory of evolution."

development

n.

1756, "an unfolding;" see develop + -ment. Of property, with the sense "bringing out the latent possibilities," from 1885 (Pickering's glossary of Americanisms, 1816, has betterments "The improvements made on new lands, by cultivation, and the erection of buildings, &c."). Meaning "state of economic advancement" is from 1902. Meaning "advancement through progressive stages" is 1836.